Effectiveness of concrete confinement on lap splice performance in concrete beams under reversed inelastic loading

Abstract

Proposals from Cornell University for seismic design of lap splices, where the strength provided to the lap splice by the concrete confinement is considered insignificant, were evaluated. The concrete confining the splice length is assumed to deteriorate after high-intensity (inelastic) reversed load cycling so that the performance is mainly dependent on the amount of transverse reinforcement provided to confine the lap splice. Lap lengths of 30–40 bar diameters are proposed, along with heavy transverse reinforcement. Longer lap lengths are considered to be less effective. By contrast, for static loading the concrete confining the splice is known to play a major role in transferring load between the bars along the splice.The current program consisted of testing six reinforced concrete beams under fully reversed cycled loading. The three similar beams in each of the two series contained equal stirrup confinement (number of stirrups) along the lap length to satisfy the Cornell University recommendations for seismic loading for the measured reinforcing yield strength, while the splice length was varied. Splices were located in the bottom face of the test beams and were positioned in a region of maximum moment to ensure severe stressing. Each series of specimens exhibited only small strength gains with increasing splice lengths; however, the performance, when evaluated on the basis of the ductility achieved and the hysteretic energy absorbed prior to failure, was superior with long splices. Since the main reinforcement in the test beams was loaded past yielding, large increases in deformation capacity resulted in only small increases in load.Full reversal inelastic load cycling is very detrimental to the concrete that confines the splice region when compared to static (monotonic) loading or one-directional repeated loading to failure. Splice failure loads under reversal loading in the current study were below predicted static strengths for the same beam configurations, and with the longer lap lengths, static failure would have been flexural rather than in the splice. Key words: reinforced concrete, beams, splices (lap), confinement, seismic design, cycled loading, ductility, strength.